With the recent development of electronics technology, electronic component modules have been widely used which are obtained by, for example, mounting surface-mount electronic components onto circuit boards.
Further, for mounting the surface-mount electronic components (hereinafter, simply referred to as electronic components) onto the circuit boards, external terminals of the electronic components are mechanically and electrically connected to mounting electrodes (objects to be connected) provided on circuit boards with the use of conductive joint materials.
As such a joint material, Japanese Patent Application Laid-Open No. 2013-91835 suggests a sinterable joint material of a liquid or paste including copper nanoparticles of 1000 nm or less in particle size, where particle size peaks in the particle size distribution on the basis of the number of the copper nanoparticles include one or more peaks in each of a zone of 1 to 35 nm in particle size and a zone of more than 35 nm and 1000 nm or less in particle size, and the copper nanoparticles include primary particles and secondary particles of primary particles fused.
Furthermore, Japanese Patent Application Laid-Open No. 2013-91835 discloses the above-mentioned sinterable joint material containing a dispersant (dispersion stabilizer), and discloses an atmosphere of hydrogen, formic acid, or ethanol as a reducing atmosphere in a firing step.
Japanese Patent Application Laid-Open No. 2013-91835 also discloses applying a sintering heat treatment while applying pressure in the direction of joining an electronic component, in the case of joining the electronic component with the use of the sintering joint material.